Planning to build a new large shed.

[Mike]

I'm planning on building a new large shed, hopefully with low heating requirements and a steady temperature all year round to enable me to use it for woodworking projects.

To keep the heat loss down to a minimum I'm going to use a high level of insulation in the walls floor and ceiling but even after reading a load of literature. I can't work out if what I'm doing is going to be ok.

With regard to the walls, the studs will probably be 89 x 38 CLS on a

600mm spacing with 12mm ply on the inner wall. The insulation will be 75mm foil covered celotex, with a tyvek outer breather layer and fibre cement weatherboard on the outside to try and make it meet fire regs (class 0)

Do I need a vapour barrier behind the inner ply?

Do I leave the gap caused by the difference in wall stud depth and insulation depth on the hot side next to the ply or on the cold side towards the tyvek or doesn't it matter?

The shed will be around 0.5m from a shared boundary fence and at least

5m from any existing structures. Will a mainly timber frame structure covered in fibre cement weatherboarding (with a green roof of sedums) meet class 0 standards or will I need plasterboard on all the inner surfaces?

[andy]

Pretty much what I did except I used ship lap for the cladding mounted on 2x1 batten nailed to the studs with the building paper held to the studs by the battens. This gives ventilation behind the ship lap.

I had the gap due to the wall insulation nearest the outside with the foil side out (only one side of mine is foil covered). Then a poly membrane which I am told is not strictly necessary but I did it anyway and the 12mm ply. It worked really well.

I also have a warm deck roof constructed with 105 mm tissue faced kingspan and a three layer built up felt roof on top. Saves having to ventilate the roof space.

I have no idea about the class 0 fire regs I am afraid but wait for others comments with interest.

Andy

[Hugo Nebula]

When you say 'large', anything with a floor area more than 15m^2 that close to the boundary will require a Building Regulations application. Also check about Planning. If it were more than 1m from a boundary, it could be up to 30m^2 and still be exempt from Building Regulations.

Building Control will be concerned about structure, external fire spread, resistance to moisture, and ventilation (amongst other things).

Roofs within 6m of a boundary must be class AA rating, ie, non-combustible. Vegetation can dry up and represent a risk of fire spread. External walls must be of 30 minutes fire resistance within 1m of the boundary, which means in your case that you will need plasterboard on the inside, as well as the non-combustible cladding.

The thermal insulation requirements do not apply to a free-standing building of less than 50m^2.

A timber framed building should have a vapour barrier on the warm side of the insulation. The plywood or other sheathing should be on the outside of the studs, with breather membrane to the outside of that, and a ventilated and drained cavity inside of the cladding.

[Tim S]

Hugo Nebula coughed up some electrons that declared:

From my research, >5m (as mentioned by the OP) from the existing house avoids the building being deducted from permitted development, weird stuff like conservation areas notwithstanding.

Thanks for the heads up on the 1m rule. I've had a b***er of a job trying to find a site for my proposed shed/workshop that get's by on a "no permission" basis.

Although I've not seen many sheds that aren't against a boundary (or certainly withing 0.5m) - have you ever known anyone be busted for such an offence?

That's useful to know.

Cheers

Tim

[<me9]

The regulations have recently changed (from October?). My first reading seems to indicate that the permitted development limit (of a percentage of the original size) was no longer there. Can anyone clarify on this?

[Tim S]

[e-mail] coughed up some electrons that declared:

I think permitted development is still there in general - it had better be because I've got 40m3 of PD left and I plan to use it. The scope of buildings in the garden changed a bit - I did notice that. You can stick solar and ground source heat pumps in now as a permitted activity but you may need permission for certain types of driveways (water runoff).

Cheers

Tim

[Tim S]

Tim S coughed up some electrons that declared:

BTW - have a look at this:

PS

From the planning portal, the section on sheds:

" Under new regulations that came into effect on 1 October 2008 outbuildings are considered to be permitted development, not needing planning permission, subject to the following limits and conditions:

• No outbuilding forward of the principal elevation fronting a highway. * Outbuildings and garages to be single storey with maximum eaves height of 2.5 metres and maximum overall height of four metres with a dual pitched roof or three metres for any other roof. * Maximum height 2.5 metres within two metres of a boundary. * No verandas, balconies or raised platforms. * No more than half the area of land around the "original house"* would be covered by additions or other buildings. * In National Parks, the Broads, Areas of Outstanding Natural Beauty and World Heritage Sites the maximum area to be covered by buildings, enclosures, containers and pools more than 20 metres from house to be limited to 10 square metres. * On designated land* buildings, enclosures, containers and pools at the side of properties will require planning permission. * Within the curtilage of listed buildings any outbuilding will require planning permission.

*The term "original house" means the house as it was first built or as it stood on 1 July 1948 (if it was built before that date). Although you may not have built an extension to the house, a previous owner may have done so."

[<me9]

Looks like no limit on permitted development other than the half of original plot size. I've already used mine up so I would have needed permission to add a conservatory. It looks as if I can now go ahead without.

[Mike]

I'd deliberately planned it to be a smidgen under the 15m2 floor area

1m from the boundary would place it too close to an existing garage to use the path (it's a very narrow site)

I really don't want to involve building control at all, the nearest approach to any existing property besides the brick built detached garage is over 5m

A green roof soaked with rainwater water and covered in soil and sedum's will be just about non combustible - that it will sit on a flammable fibreglass laminate over OSB ought to be irrelevant - surely normal roofing felt will easily burn?

Plasterboard on the inside is completely unacceptable, I want to use it for a shed/workshop not a living space!

They might not, but I'm reluctant to pay a fortune to heat or cool this space when a few inches of celotex will keep it snug in winter and cool in summer.

That *normally* being the plasterboard (foil backed?)

I'll not be using that, 12mm ply as a minimum so I can hang things on the wall. .

Well I'd not planned for anything to be on the outside except the fibre cement weatherboarding

The breather membrane surely goes under the outside layer?

If the moisture barrier is on the inside, using foil backed plasterboard or in this case probably plastic sheet, then surely any moisture in the cavity on the outside of the celotex permeates through the breather layer into the atmosphere. Venting the cavity to the inside is surely the last thing to do, it permits moisture from activity in the shed into the cavity which may then condense on cold insulation.

[Mike]

Good, it's in the back garden

I'm aiming for minimum 2.1m clear height inside so with a few inches of insulation in the rood I'll be way less than 2.5m

It's a shed :)

No problem there

None of which apply

*

None of which apply

Just concerned that the some overriding building regs legislation will interfere with my plans on proximity to the boundary.

[Hugo Nebula]

Then everything else is moot.

I think you may have misunderstood.

Firstly condensation is greater on the inside of a building than the open air, so you want a vapour barrier to prevent it migrating through to the structure. Whether plywood would suffice for this purpose I'm not sure; it's not something that's normally done, because...

Secondly, sheathing is usually provided to the outside of the studwork for structural reasons; where it's not structural, it's better to have a more permeable material. The sheathing is also something to fix the breather membrane against.

A breather membrane forms a water-resistant layer to the outside of the 'inner leaf' structure, that can still allow vapour from the inside through.

There should always be a cavity between the membrane and the outer cladding (which in your case is the fibre cement boards). If not you run the risk of any water getting in, and any vapour getting out, not being able to drain away.

But, hey! Building Regulations don't apply, so feel free to build it how you like.

[news]

I looked into green roofs last year, you should be aware that it will weigh in at 45 kilos a square metre. Chris